1. Field of the Invention
The present invention relates to a wireless broadband (WiBro) communication system and, in particular, to a connection control system and method for WiBro communication system.
2. Description of the Related Art
Wireless Broadband (WiBro) is a wireless broadband Internet technology developed for providing a high-speed data service in stationary environments, pedestrian-speed environments, and mobile environments at speeds below 60 Km/h. The WiBro provides an Internet Protocol (IP)-based asynchronous wireless data transmission service by adopting Orthogonal Frequency Division Multiple Access (OFDMA) for multiple access and Time Division Duplex (TDD) for duplexing.
In order to receive the WiBro service, a mobile terminal must be connected to a WiBro Radio Access Station (RAS).
During a network connection procedure, the mobile terminal selects a cell, synchronizes PHYsical layer (PHY) with an RAS of the selected cell, and receives downlink and uplink parameters through a DownLink Mobile Application Part (DL-MAP) and an UpLink Mobile Application Part (UL-MAP). The mobile terminal then transmits an initial RaNGing REQuest (initial RNG-REQ) message to the RAS and receives an initial RaNGing ReSPonse (initial RNG-RSP) message from the RAS in response to the initial RNG-REQ message. If the initial RNG-RSP message is received, the mobile terminal performs a capability negotiation with the RAS. During the initial ranging procedure, the mobile terminal starts a timer at the same time with the transmission of the initial RNG-REQ message and performs, if the timer expires before receiving the initial RNG-RSP message, the network connection procedure again, i.e. reconnection procedure.
Such a network connection procedure is normally processed in a single cell environment. However, some problems may occur when the mobile terminal is located in an area where at least two cells are overlapped and tries to connect to the network.
For example, when a mobile terminal associated with a serving RAS moves into a handoff area, the mobile terminal may not receive an RNG-RSP message in response to the initial RNG-REQ message, especially when the mobile terminal enters another cell defined by a handoff target RAS. In this case, the mobile terminal must perform the network connection procedure with the target RAS again.
As explained above, since the network connection procedure of the conventional WiBro system requires a redundant network connection procedure, connection delays and user discomfort occur, especially when the mobile terminal attempts an initial ranging in a handoff area.